docs: def _getNextArticleBatch(self):
          """download next batch of articles based on the article uris in the uri list"""
          # try to get more uris, if none
          self._articlePage += 1
          # if we have already obtained all pages, then exit
          if self._totalPages != None and self._articlePage > self._totalPages:
              return
          self.setRequestedResult(RequestArticlesInfo(page=self._articlePage,
              sortBy=self._sortBy, sortByAsc=self._sortByAsc,
              returnInfo = self._returnInfo))
          if self._er._verboseOutput:
              print("Downloading article page %d..." % (self._articlePage))
          res = self._er.execQuery(self)
          if "error" in res:
              print("Error while obtaining a list of articles: " + res["error"])
          else:
              self._totalPages = res.get("articles", {}).get("pages", 0)
          results = res.get("articles", {}).get("results", [])
          self._articleList.extend(results)